Abstract: A Rotating Stress Field and the Evolution of Basins in the Gulf of Thailand

Steven Harder, Robert McCabe, Martin Flower

A glance at a sediment thickness map indicates that the Gulf of Thailand contains a variety of basin orientations. Even more unusual is that these basins were formed during a short time period (Eocene to Oligocene). We relate this variety of extensional orientations to events on the margins of southeast Asia.

Northwest-southeast, and in some areas east-west directed extension began in the Con Son and surrounding basins during the Eocene. This extension was probably related to that in the South China Sea and involved motion on northwest-southeast-trending strike-slip faults. However, the extension axis soon rotated to a more north-south orientation forming the Malay Basin producing continued subsidence in existing basins. This stress field rotation coincides with the time when the India-Asia collision became more forceful. Stress field rotation continues as India slides past the western margin of southeast Asia, with extension becoming east-west as India moves farther north. This east-west-directed extension formed north-south trending basins both offshore and later onshore in Thailand.

Because the Thai basins were formed under east-west extension, they place strict limits on the location and timing of collision related extrusion in southeast Asia. East-west extension in Thailand cannot begin until east-west compression driving the extrusion of southeast Asia migrated well north of the area undergoing extension. This means that northern Thailand, where east-west extension began in the late Oligocene, was well clear of the collision by the middle of the Oligocene.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994